The Museum of HP Calculators

Calculator Comparison

Features in optional ROMs are listed as Option.
Features in HP mag card or tape Application Pacs are listed as +.
Other software is not included.
Display and Keyboard HP-15C HP-42S
Display type LCD LCD
Display format 1 Line 2 Line
FIXed number format Yes Yes
SCIentific number format Yes Yes
ENGineering number format Yes Yes
STanDard / ALL number format - Yes
Alpha messages and prompts - Yes
Softkeys labeled by mag. card or overlay - -
Softkeys labeled by display menus - Yes
Softkeys with neither labeling system Yes -
Status annunciators Yes Yes
Redefinable keyboard - Yes
Logic HP-15C HP-42S
Logic system RPN RPN
Stack levels 4 4
Last x Yes Yes
Undo - -
Precedence - -
Parentheses - -
Storage Addition (STO +) Yes Yes
Storage Arithmetic (STO +, −, ×, ÷) Yes Yes
Storage Exponentiation (STO ^) - -
Recall Arithmetic Yes Yes
Named variables - Yes*
Multiple data types - Yes*
Directories - -
Math HP-15C HP-42S
+, −, ×, ÷ Yes  Yes 
1/x Yes Yes
√ Yes Yes
x2 Yes Yes
LOG x Yes Yes
10x Yes Yes
LN x Yes Yes
ex Yes Yes
yx Yes Yes
π Yes Yes
% Yes Yes
% change Yes Yes
INTeger truncation and ABSolute value Yes Yes
Trigonometric functions (SIN, COS etc.) Yes Yes
Hyperbolic trig. (SINH, COSH etc.) Yes Yes
# of trig. modes (degrees, radians, grads) 3 3
Advanced Math HP-15C HP-42S
Solver / root finder Yes Yes
Numeric integration Yes Yes
Complex numbers Yes Yes
Matrix operations Yes Yes
Matrix writer - -
Equation writer - -
Symbolic operations - -
Fractions - -
Plotting and graphics (display) - Yes
Plotting and graphics (printer / plotter) - Option
Statistical HP-15C HP-42S
Mean, standard deviation (# of variables) 2 2
Σ of n, x, x2 Yes Yes
Σ of n, x, x2, y Yes Yes
Σ of n, x, x2, y, xy Yes Yes
Σ of n, x, x2, y, y2, xy Yes Yes*
Σ of lists - -
Random number generator Yes Yes
Linear regression, estimate  Yes Yes
Curve fitting - Yes
Correlation coefficient Yes Yes
Normal distribution - -
Factorial Yes Yes
Gamma Yes Yes
Combinations and permutations Yes Yes
Scientific and Time HP-15C HP-42S
Polar / rectangular conversions Yes Yes
Base conversions (2, 8, 10, 16) - Yes
Arithmetic in bases 2, 8 and 16 - Yes
Bit operations (AND, OR, XOR, ...) - Yes
Selectable word size (1-64 bits) - -
Selectable complement mode (1's, 2's, unsigned) - -
Decimal hrs / hrs.min.sec. conversions Yes Yes
Hrs.min.sec arithmetic - Yes
Time of day clock - -
Timer - -
Dynamic calculations (timer × rate) - -
Alarms - -
Unit Conversions HP-15C HP-42S
Centimeters / inches - -
Millimeters / inches - -
Meters / feet - -
Kilograms / pounds (mass) - -
Newtons / pounds (force) - -
British thermal units / joules - -
Liters / gallons - -
° Celsius / ° Fahrenheit - -
Other - -
User-defined units - -
Time Value of Money HP-15C HP-42S
Number of payments (n) - -
Interest rate (i) - -
Present Value (PV) - -
Payment (PMT) - -
Future Value (FV) - -
Cash Flow Analysis HP-15C HP-42S
Net present value (NPV) - -
Internal rate of return (IRR) - -
Amortization HP-15C HP-42S
Accumulated Interest (ACC INT) - -
Balance (BAL) - -
Depreciation HP-15C HP-42S
Straight line (SL) - -
Sum of the years digits (SOYD) - -
Declining balance (DB) - -
Bonds and calendar functions HP-15C HP-42S
Bond price - -
Bond yield - -
Date arithmetic / calendar functions - -
Memory and Programming HP-15C HP-42S
Programming language(s) RPN RPN
RAM / Max # of variables or addressable registers 67 7200 bytes /
895 registers
Max # of program steps 448* 7200*
RAM / Max vars or regs with full optional RAM - -
Max # of prog steps with full optional RAM - -
Merged program steps  Yes Yes
Manual register / program memory allocation  Yes Yes
Automatic register / program memory allocation - -
Overlapped register and program memory - -
Continuous memory Yes Yes
Flags 10 100
Conditional tests 12 12
Subroutine levels 7 8
Indexed looping (increment by +/- 1, end at 0) Yes Yes
Indexed looping (choice of increment and end) Yes Yes
Multiple index / loop registers Loop only Yes
Line number addressing Via I* -
Branching by relative line number - -
Global program label addressing Yes Yes
Local program label addressing - Yes
Indirect / computed addressing and control Yes Yes
Multiple indirection registers - Yes
Pause Yes Yes
Alpha messages and prompts in programs - Yes
Alpha program listings - Yes
Alpha string manipulation - Yes
Program step insert / delete Yes Yes
I/O and Expansion Features HP-15C HP-42S
ROM modules - -
RAM modules or expansion option - -
General expansion slots / connector - -
Magnetic card reader/writer - -
Tape drive - -
Disk drive - -
Upgradeable firmware - -
Optical wand - -
Serial port - -
Infrared input - -
Infrared output - Yes
Printer - Option
Networking - -
Other - -
General HP-15C HP-42S
Sounds - Yes
Self test Yes Yes
Hard case (in addition to soft case) - -
Additional Features - -
Batteries 3 SR44 3 SR 44
Length (inches) 5.1" 5.85"
Width 3.1" 3.15"
Height 0.6" 0.6"
Weight (oz or lbs) 4 oz 5 oz
Year of introduction 1982 1988
Features in optional ROMs are listed as Option.
Features in HP mag card or tape Application Pacs are listed as +.
Other software is not included.

Unlim means limited only by available memory.
HP-15C notes:
  • The HP-15C had enough memory for 448 one-byte instructions but some instructions required two bytes.
  • If the number in the I register was negative, the calculator branched to the line number indicated by the absolute value of that number.
  • Self test: with the calculator off, hold the × key down and press and release ON, then release ×. The calculator will display running for around half a minute and then activate the entire display to indicate success. The test may be done continuously by (with the calculator off) holding + down while pressing the ON key. To stop the continuous test at the end of the current iteration, press and hold − and then press ON.
  • There is also a keyboard test. With the calculator off, press and hold ÷ and press ON. Now press each key from the top left moving left to right and then down (the enter key gets pressed in both the third and fourth rows.) If all keys are pressed in the correct order and are working, the model number (without the C) is displayed. Otherwise, Error 9 is displayed. (The display will show a changing pattern of segments as keys are pressed.)
HP-42S notes:
  • Named variables AND numbered registers.
  • Manual presented basic Time Value of Money formula as an example of using the Solver.
  • Besides n, x, x2, y, y2, xy, the calculator also summed: ln x, (ln x)2, ln y, (ln y)2, ln x × ln y, x ln y, and y ln x
  • Data types were real, complex, string and alpha. Any type could be stored in the stack or in a variable, but only single numbers could be stored in numeric registers and you had to convert all registers to complex to store a complex number in any register.
  • Maximum number of program lines assumes no registers and only single byte instructions.
  • To start the self test, with the calculator on, press and hold the LOG key and press the ON/EXIT key. Pressing the + key will step through a series of tests (including printing a copyright) until you see KBD. Then you must press each key from the upper left from left to right and then down until you see KBD OK. Pressing + will show OK-42S-E. If there is a problem, you will see a FAIL message. To exit the test, at any point, press and hold the √ key and then press the ON/EXIT key. Instead of stepping through the general tests, you can start some specific self tests after pressing LOG+ON/EXIT by pressing:
    • Σ+: Speed
    • 1/x: Beep
    • √: DISP
    • LOG: ROM
    • LN: DRAM
    • XEQ: URAM
    • RCL: ESD (electro-static discharge test?)
    • STO: KBD
    • R↓: Displays the OK message
  • A continuous test (minus the keyboard test) can be started by holding 1/x and pressing ON/EXIT. Exit this test in the same way as the individual test.

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